1. Field of the invention
This invention relates to a thin type electric cell used for reducing the size and weight of a portable electric equipment. More particularly, it relates to an electrode terminal structure thereof.
2. Description of Related Art
Recently, an electric cell has come to play a crucial role industrially as a power source for portable electrical equipments. For reducing the size and the thickness of the equipments, there is raised a demand for the cell to be able to be housed in a limited space in the equipment. For this purpose, a lithium cell having high energy density and high output density is thought to be most appropriate.
On the other hand, for reducing the size and the weight of the equipment, such a cell which is flexible and high in the degree of freedom in morphology, thin in thickness and large-sized in area or which is thin in thickness and small-sized in area, is desired. These requirements, however, cannot be met if a conventional metal can is used as an outer packaging member. In particular, with a moisture-proofing type multi-layered film, comprised of a heat-fusion type high molecular weight film layer and a metal foil layer, a heretically sealed structure can be realized by hot sealing, while the film itself has superior strength and air-tightness. Thus, the moisture-proofing type multi-layered film is promising as a candidate for the outer packaging material for a cell having high degree of freedom in morphology or a thin type cell.
However, in establishing electrical conduction between the electrode and the external terminal in the moisture-proofing type multi-layered film, through an electrode terminal at a sealing opening of the outer packaging material, the thin sealing opening cannot be sealed with a thick metal wire, while a fine metal wire by itself cannot assure sufficient conductivity. The sealing opening can be reduced in thickness, while conductivity can also be provided, if a metal foil is used for the electrode terminal. However, sufficient tightness in adhesion cannot be provided between the heat fusion type high molecular weight film layer and the metal foil (electrode terminal). The result is that application of the slightest stress leads to delamination to render it impossible to maintain air-tightness of the cell.
Thus, with the electrode terminal of a metal wire or a metal foil, satisfactory air-tightness or mechanical strength cannot be achieved. In particular, the lithium cell, for which investigations are proceeding briskly because of the high energy density and high output density, and which has a sufficient moisture-proof construction is required to be high in air-tightness.